1. Field of the Invention
The invention relates generally to the design of flapper valves.
2. Description of the Related Art
A flapper valve is a plate-like member that is pivotally affixed to one side of the tubing string and may be rotated 90 degrees between an open position and a closed position. A spring member typically biases the flapper element toward its closed position. The flapper element is typically opened using hydraulic fluid pressure.
Flapper valves have a variety of downhole uses, including safety valves. In addition, flapper valves can be incorporated into fluid loss control valves and wellbore isolation valves. In such instances, the flapper valve is installed in an inverted position so that the flapper element opens by being pivoted upwardly (toward the opening of the well).
At times, it is necessary to reopen a flapper valve after it has been closed. However, if the hydraulic system for opening the flapper valve should fail, there is a lack of reliable backup means for opening the flapper element. In prior art techniques, a pipe or other tubular member is brought into engagement with the flapper element to push it off of its valve seat and rotate the valve member to its open position. An example of this is described in U.S. Pat. No. 6,705,593 issued to Deaton. However, this opening mechanism is not useful where the flapper element opens upwardly (i.e. toward the surface of the wellbore). In that case, urging a tubular member against the valve member would only force the valve assembly closed.
The present invention addresses the problems of the prior art.